1. Field of the Invention
The present invention relates to a three-dimensional image display device, more specifically to a three-dimensional image display device creating an effect of three dimensions by displaying an enlarged two-dimensional image as a three-dimensional form with real depth in the air, using a transmissive screen, displayed through the image source, a reflector (or reflectors), and a double Fresnel lenses structure.
2. Description of the Related Technology
Three-dimensional display refers to a technology using, for example, the stereoscopic technology to add depth to two-dimensional images and using this depth to allow the viewer to feel the sense of animateness and reality. Various types and methods of conventional three-dimensional display devices have been suggested using these technologies. Most of these technologies have displayed three-dimensional images using the difference in visual angles between left and right eyes. A typical form of this application separates the left and right images, mainly with or without using eyeglasses.
Using glasses are an anaglyph method, a polarized glasses method, and a liquid crystal shutter method, while without glasses are a lenticular sheet method, a parallax barrier method, and an optical plate method. Among these conventional methods, the polarized glasses method has been the oldest and most widely used, utilized in three-dimensional (3D) movies and 3D monitors owing to its stability. The weakness of this method, however, lies in the requirement of using special polarized glasses for three-dimensional images. The lenticular sheet method and parallax barrier method, not using eyeglasses, have problem of low brightness and resolution, and causes headaches or dizziness when viewed for an extended period of time. While the holographic method and volumetric 3D display method can realize three-dimensional images freely in the air, they require expensive laser and precision optical components to display even a still image, and can not provide real-time three-dimensional images.
As means for solving these problems, some of the non-glasses methods have utilized reflectors, general optical lenses, and concave mirrors to enable real-time three-dimensional images at lower costs. However, these methods experience distortion of images due to the concave of the mirrors and high costs of manufacturing due to their large size. The need for a large space particularly, if a large screen is desired, has been largely complicating the application and commercialization of these methods.
In addition to these methods using concave mirrors and reflectors, the methods, using Fresnel lenses have been variously proposed for a long time. U.S. Pat. No. 3,537,771 discloses that two Fresnel lenses can be used to provide a three-dimensional image effect, and U.S. Pat. No. 5,782,547 discloses that one, two, or more Fresnel lenses and reflectors can be used to create various forms of three-dimensional images. These methods, however, require large transmissive reflectors and two or more image sources in order to realize a three-dimensional image on a large screen, resulting in higher manufacturing costs and hefty spatial design.
U.S. Pat. No. 6,055,100 realizes large screen three-dimensional images using 2 Fresnel lenses and a liquid crystal projector, but practical display of three-dimensional images is restricted by the distortion of three-dimensional images, created for a wide-angle view, and the limitation in image size.
Referring to FIG. 1, which shows a three-dimensional display device based on prior art, a two-dimensional image is projected from an image source supply unit 4 along projection lines 7, 8 and formed on a reflective screen 5 before being projected toward Fresnel lenses along projection lines 9, 10. A first Fresnel lens 1 and a second Fresnel lens 2 work in combination like a single lens to project an image along projection lines 11, 12 to a focal plane 6 within a focal length 13 of double Fresnel lenses 3. In order to display a large size three-dimensional image, there needs to be a substantial distance between the first Fresnel lens and an image projected to the screen from the image source supply unit 4 to obtain a desired three-dimensional image on the focal plane 6. The image projected to the reflective screen 5 becomes a convex screen of a semi-spherical shape by forming the three-dimensional image on the focal plane 6 to face the direction of the grooves of first and second Fresnel lenses. The semi-spherical focal plane 6 uses only a quarter of the entire screen size of the second Fresnel lens, and the image from the image source 4 is distorted toward the fringe of the focal plane 6. Moreover, the semi-spherical focal plane, formed by the double Fresnel lenses, has a sharp circular boundary, lessening the sense of depth.
U.S. Pat. No. 6,375,326 discloses a method of using a Fresnel lens and a reflector to achieve the same effect as using two Fresnel lenses, but it also requires a large space between the top and bottom as well as the front and back, compared with the screen size of the three-dimensional image, when large three-dimensional images are desired. The shortened projection distance, owing to the adaptation of a reflector, also reduces the sense of depth.
As described so far, the conventional methods experience problems of high manufacturing costs, when large three-dimensional images are desired, and distortion of images, as well as a large projection space needed when the device is made larger. As these problems are inherent properties of Fresnel lenses, the image source must be separated proportional to the focal length of the Fresnel lens, the spherical formation of the three-dimensional image distorts the fringe of an image due to the image source screen being a two-dimensional plane behind the double Fresnel lenses, the inherent reflective property of Fresnel lenses creates virtual images, and the reflection of external light shallows the depth of three-dimensionality.